Electro-optical semiconductor devices, such as laser or semiconductor diodes or detectors, are enclosed in hermetically sealed packages for protection and ease of alignment of the device with, for example, optical fibers. A light-transmissive window must be present in the package to allow light to pass into or out of the package.
When the devices are to be used in outer space, for example, where large amounts of high energy levels of radiation are present, the material of the window must be resistant to discoloration, degeneration or other degradation of its optical transmission properties in the presence of radiant energy.
In addition, the windows must be able to be coated with standard anti-reflection coatings and to be brazed or otherwise cemented into the package without physical distortion or undue stresses being imparted to the window material.
In the past quartz has been employed as a window material for optical device packages because quartz does not discolor in the presence of high levels of atomic radiation. However, its thermal expansion coefficient is lower than most metals, so it has not been possible to braze metal seals to the quartz without significantly distorting or warping the quartz window, particularly over the broad temperature ranges encountered in hermetic-seal brazes.